Climate and landscape modification facilitate range expansion in Spinus psaltria (Lesser Goldfinch) across the Pacific Northwest

Abstract

Spinus psaltria (Lesser Goldfinch) has undergone significant range expansion throughout the Pacific Northwest in recent decades, expanding farther northward through Oregon, Idaho, and Washington. We used data from Project FeederWatch to reveal a 3.94 decimal degree or ~437.34 km northward expansion in occupancy from 2002 to 2022, with eBird Status and Trends indicating that breeding season populations increased significantly in Oregon (16.9%), Idaho (66.3%), and Washington (110.5%) from 2012 to 2022. We found that S. psaltria was more likely to colonize sites within their expanded range that had higher maximum annual temperatures and annual rainfall, increased surrounding urban development, and closer proximity to major rivers. Additionally, our models showed sites typically remained occupied once colonized, indicating permanent range expansions rather than temporary nomadic movements. Our study highlights how S. psaltria's range in the Pacific Northwest is shaped by both climate and landscape characteristics and reflects broad ecological responses to climate change and habitat modification, suggesting continued expansion as these factors persist.